It is well known in the field of microwave heating that it is necessary to provide means to confine microwave energy within a heating cavity or enclosure. Such requirements include the use of sealing arrangements between the cavity and the door covering the entrance thereto in order to reduce microwave transmission or leakage at that interface to a minimum.
Various sealing arrangements have been suggested in the art. These include absorptive seals, contact seals and choke seals. Absorptive seals typically place microwave energy absorptive material in the area of the cavity-door interface to absorb microwave energy reaching that area. Contact seals provide electrical, typically metal-to-metal, contact between the door and the cavity to prevent passage of microwave energy. Choke seals employ the principle of a short circuited microwave transmission line, making use of known characteristics of microwave energy occuring at various 1/4 wave length intervals.
In recent years it has proven desirable to incorporate heating by both conventional thermal means and by microwave energy into a single cavity, such as in a free standing range. Since such an appliance can accomplish heating and cooking by conventional means, it is subject to the hard soiling found in conventional ovens. It is therefore desirable to make such an appliance selfcleaning, which may in turn encompass the use of temperatures well above the normal cooking level to accomplish cleaning by controlled pyrolysis. The presence of temperatures in the pyrolytic temperature cleaning range renders many methods and materials commonly used in microwave appliances unsuitable for a combination thermal/microwave oven.
One solution that has been suggested is the use of a contact seal accomplished with a gasket of metallic mesh captured between the door and the oven cavity. Such an arrangement has serious disadvantages. Good sealing depends upon continuous contact around the entire periphery of the door which is difficult to accomplish initially, and more difficult to maintain as the appliance is used and the gasket is subject to wear. Moreover, such appliances are conventionally made of porcelainized steel, and the porcelain finish is a sufficient electrical insulator to prevent electrical contact. Therefore, in such prior art arrangements it was necessary to apply a special metallic coating to the peripheral area in contact with the gasket.
An arrangement consisting of a combination of all three types of seals has been suggested in the prior art. While such an arrangement may be effective in preventing microwave leakage, it is also more complex and expensive than is commercially desirable.
It is therefore an object of the present invention to provide an effective door seal apparatus to prevent the leakage of microwave energy from a cooking cavity, which apparatus is capable of withstanding exposure to pyrolytic cleaning oven temperatures without detremental effect on its performance.
Another object of the present invention is to provide a sealing arrangement for the interface between a cooking cavity and the cavity door which is effective in preventing the escape of significant levels of microwave energy, is able to withstand heat cleaning temperatures in excess of 750.degree. F, and is relatively simple and inexpensive to manufacture.
A still further object of the invention is to provide a choke-type sealing arrangement including a chamber configured to discourage the accumulation of soil in and around the chamber without the use of additional components.
A still further object of the invention is to provide a microwave seal for a combination cooking appliance which seal is not subject to deterioration or diminution of effectiveness due to age or repeated use of the appliance.
Further objects and advantages to the invention will become obvious as the description proceeds.